Front face erasable microcapsule magnetophoretic writing magnet

ABSTRACT

Disclosed herein is a front face erasable microcapsule magnetophoretic display sheet having a support and a solid dispersion layer provided on one surface of the support and composed of microcapsules having an average particle diameter of 50 to 650 μm, in which a liquid dispersion, a white pigment, additives and magnetic particles are encapsulated, and a binder. The magnetic particles include at least two kinds of magnetic particles different in particle diameter from each other. An erasing magnet for front face erasing and a writing magnet for front face erasable microcapsule magnetophoretic display sheet are also disclosed.

BACKGROUND OF THE INVENTION

This application claims priority to Japanese patent application no.2001-392561 filed on Dec. 25, 2001.

FIELD OF THE INVENTION

The present invention relates to a front face erasable microcapsulemagnetophoretic display sheet, an erasing magnet and a writing magnetfor the sheet, and particularly to a front face erasable microcapsulemagnetophoretic display sheet, by which a magnetic record magneticallyrecorded on the front face of the sheet can be erased wholly orpartially from the front face side thereof by a magnet, an erasingmagnet which can erase a record from the front face side of a recordedsheet, and a writing magnet for the sheet.

RELATED BACKGROUND ART

There has heretofore been known a magnetic recording system that amagnetic recording is conducted on the front face of a microcapsulemagnetophoretic display sheet. This magnetic recording system isgenerally a system that an erasing magnet is slid on the whole rear faceof the microcapsule magnetophoretic display sheet to make the front facethereof clean, writing is then conducted on the front face with awriting magnet or magnet pen to obtain a magnetic record, and themagnetic record recorded thereon is optionally erased from the rear faceside by sliding an erasing magnet on the whole rear face thereof. Whensuch a magnetic record is erased, the erasing magnet is slid on the rearface of the microcapsule magnetophoretic display sheet, thereby erasingthe record recorded on the front face of the magnetophoretic displaysheet. According to an erasing method heretofore used, however, themagnetically recorded display recorded on the microcapsulemagnetophoretic display sheet is erased at the whole portion slid by theerasing magnet when the erasing is conducted from the rear face side.Therefore, only a desired portion of the magnetically recorded displaycannot be erased, which is very inconvenient. The uses thereof are thuslimited.

SUMMARY OF THE INVENTION

Once characters, diagrams and/or the like magnetically recorded can beerased from the front face side under the foregoing circumstances, therecord can be partially erased, to say nothing of the whole surfaceerasing, so that not only such inconvenience as described above can beeliminated, and such a microcapsule magnetophoretic display sheetbecomes easy to use, but also excellent merits that the sheet can beapplied to various uses, for example, chalk boards, and used byattaching it on surfaces of walls, lockers, etc. or for production ofmachine readable magnetic records and as inspection materials of steelproducts or the like can be achieved. The present inventors have paidattention to this regard and continued to carry out variousinvestigations. As a result, it has been found that the microcapsulemagnetophoretic display sheet is improved, and the erasing magnet andthe writing magnet or magnet pen is devised, whereby printing ofrecorded characters and the like or erasing of the print can bepartially and easily conducted from the front face of the magneticdisplay sheet. It is therefore a first object of the present inventionto provide a front face erasable microcapsule magnetophoretic displaysheet, by which characters, diagrams and/or the like magneticallyrecorded on the front face of the magnetic recording sheet can be simplyand easily erased wholly or partially from the front face side thereof.

A second object of the present invention is to provide an erasing magnetfor front face erasing, which has a simple structure and can wholly orpartially erase characters, diagrams and/or the like from the recordingsurface side of a recorded sheet.

A third object of the present invention is to provide a writing magnetfor front face erasable microcapsule magnetophoretic display sheets, bywhich fine characters, diagrams and/or the like can be clearlydisplayed.

The above objects of the present invention can be achieved by therespective aspects of the present invention described below.

According to the present invention, there is thus provided a front faceerasable microcapsule magnetophoretic display sheet comprising a supportand a solid dispersion layer provided on one surface of the support andcomposed of microcapsules having an average particle diameter of 50 to650 μm, in which a liquid dispersion, a white pigment, additives andmagnetic particles are encapsulated, and a binder, wherein the magneticparticles include at least two kinds of magnetic particles different inparticle diameter from each other.

In the front face erasable microcapsule magnetophoretic display sheetdescribed above, at least one kind of magnetic particles having aparticle diameter ranging from 0.1 μm to 1.0 μm and at least one kind ofmagnetic particles having a particle diameter greater than the aboveparticles ranging from greater than 1.0 μm to 20 μm may be used as themagnetic particles.

In the front face erasable microcapsule magnetophoretic display sheetdescribed above, the proportion of the magnetic particles may be the sumtotal of 100% by weight of said at least one kind of magnetic particleshaving a particle diameter ranging from 0.1 μm to 1.0 μm and 10 to 200%by weight of said at least one kind of magnetic particles having aparticle diameter greater than the above particles ranging from greaterthan 1.0 μm to 20 μm.

In the front face erasable microcapsule magnetophoretic display sheetdescribed above, the support may be a releasing member, and the displaysheet is composed of only a support-free solid dispersion layer fromwhich the releasing member has been released and removed.

In the front face erasable microcapsule magnetophoretic display sheetdescribed above, a solvent in the liquid dispersion may be composed ofat least one low-boiling solvent selected from the group consisting oftoluene, xylene, ethylbenzene, methylcyclohexane, ethylcyclohexane andcyclohexane and at least one high-boiling solvent selected from thegroup consisting of dodecylbenzene, dipentylbenzene, diphenyl ether,dibenzyl benzoate, phenylxylylethane, diethylbenzene, pentylbenzene,ethyl phthalate and butyl phthalate, and a proportion of thehigh-boiling solvent to the low-boiling solvent may be 10 to 250 partsby weight per 100 parts by weight of the low-boiling solvent.

According to the present invention, there is also provided an erasingmagnet for front face erasing, which is adapted to slide it over atleast a part of the front face of a front face erasable microcapsulemagnetophoretic display sheet, wherein the magnet is arranged and usedin such a manner that a clearance is made between the front faceerasable microcapsule magnetophoretic display sheet and the magnet,whereby a magnetic field different from the case where the magnet isbrought into direct contact with the sheet acts on microcapsules in thesheet.

According to the present invention, there is further provided a writingmagnet for front face erasable microcapsule magnetophoretic displaysheets, wherein a magnet is covered with a metal to control a magneticfield.

In the front face erasable microcapsule magnetophoretic display sheetaccording to the present invention, comprising the support and the soliddispersion layer provided on one surface of the support and composed ofthe microcapsules having an average particle diameter of 50 to 650 μm,in which the liquid dispersion, the white pigment, the additives and themagnetic particles are encapsulated, and the binder, the magneticparticles may include at least two kinds of magnetic particles differentin particle diameter from each other, whereby the magnetic sheet canexhibit a particularly marked effect that characters, diagrams and/orthe like magnetically recorded on the magnetic recording sheet can bewholly or partially erased simply and easily from the recording surfaceside thereof.

In the magnetophoretic display sheet according to the present invention,at least one kind of magnetic particles having a particle diameterranging from 0.1 μm to 1.0 μm and at least one kind of magneticparticles having a particle diameter greater than the above particlesranging from greater than 1.0 μm to 20 μm may be used as the magneticparticles, whereby the magnetic sheet can exhibit a particularlypreferred effect for wholly or partially erasing the magneticallyrecorded characters, diagrams and/or the like simply and easily from therecording surface side.

In the magnetophoretic display sheet according to the present invention,the proportion of the magnetic particles may be the sum total of 100% byweight of said at least one kind of magnetic particles having a particlediameter ranging from 0.1 μm to 1.0 μm and 10 to 200% by weight of saidat least one kind of magnetic particles having a particle diametergreater than the above particles ranging from greater than 1.0 μm to 20μm, whereby the magnetic sheet can exhibit an excellent effect that themagnetically recorded characters, diagrams and/or the like can be whollyor partially erased simply and easily from the recording surface side.

In the magnetophoretic display sheet according to the present invention,the support may be a releasing member, and the display sheet may becomposed of only a support-free solid dispersion layer from which thereleasing member has been released and removed, whereby the uses of thesheet can be variously widened without using any writing magnet pen inthat it can be used for production of machine readable magnetic recordsand as inspection materials of steel products or the like.

In the magnetophoretic display sheet according to the present invention,a solvent in the liquid dispersion may be composed of at least onelow-boiling solvent selected from the group consisting of toluene,xylene, ethylbenzene, methylcyclohexane, ethylcyclohexane andcyclohexane and at least one high-boiling solvent selected from thegroup consisting of dodecylbenzene, dipentylbenzene, diphenyl ether,dibenzyl benzoate, phenylxylylethane, diethylbenzene, pentylbenzene,ethyl phthalate and butyl phthalate, and a proportion of thehigh-boiling solvent to the low-boiling solvent may be 10 to 250 partsby weight per 100 parts by weight of the low-boiling solvent, wherebythe dispersoids can be more stably dispersed.

In the erasing magnet for front face erasing according to the presentinvention, which is adapted to slide it over at least a part of thefront face of a front face erasable microcapsule magnetophoretic displaysheet, the magnet may be arranged and used in such a manner that aclearance is made between the front face erasable microcapsulemagnetophoretic display sheet and the magnet, whereby a magnetic fielddifferent from the case where the magnet is brought into direct contactwith the sheet acts on microcapsules in the sheet. As a result, anerasing magnet for front face erasing, which has a simple structure andcan partially erase characters, diagrams and/or the like from therecording surface side of a recorded sheet can be provided.

In the writing magnet according to the present invention for front faceerasable microcapsule magnetophoretic display sheets (hereinafterreferred to as “writing magnet for front face erasable sheet”), themagnet may be covered with a metal to control a magnetic field, wherebythe writing magnet can exhibit an excellent effect that fine characters,diagrams and/or the like can be clearly displayed.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become apparent from the following description and theappended claims, taken in conjunction with the accompanying drawings, inwhich:

FIGS. 1A and 1B are a plan view and a cross-sectional view,respectively, illustrating an erasing magnet for front face erasingaccording to an embodiment of the present invention;

FIGS. 2A and 2B are a plan view and a cross-sectional view,respectively, illustrating an erasing magnet for front face erasingaccording to another embodiment of the present invention; and

FIGS. 3A and 3B are a plan view and a cross-sectional view,respectively, illustrating a writing magnet for front face erasablesheet used in the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will hereinafter be described in detail.

In the front face erasable microcapsule magnetophoretic display sheetsaccording to the present invention, at least two kinds of magneticparticles different from each other in at least any of particle diameterand material are contained. As these magnetic particles, any magneticparticles may be used so far as they are ordinarily used in thistechnical field. Examples thereof include fine particles of black ironoxide, porous iron oxide, manganese dioxide-containing iron oxide,chromium dioxide, ferrite, iron and nickel, and magnetic particles towhich no hydrophilic treatment is subjected, such as iron-nickel alloys,with synthetic magnetic iron oxide being particularly preferred. Thesemagnetic materials may be used either singly or in any combinationthereof. Examples of commercially available products include TodacolorKN-320 (magnetite, product of Toda Kogyo Corporation and Tarox BL-50(synthetic iron oxide, product Titan Kogyo K.K. Magnetic iron oxiderepresented by Fe₃O₄ is preferred.

The particle diameter of these magnetic particles are preferably notgreater than 20 μm, more preferably 0.1 μm to 20 μm. In the magneticparticle groups different from each other in particle diameter, a groupof magnetic particles having a smaller particle diameter has a particlediameter ranging from 0.1 μm to 1.0 μm, and one or more kinds of suchmagnetic particles are used. On the other hand, a group of magneticparticles having a greater particle diameter has a particle diameterranging from greater than 1.0 μm to 20 μm, and one or more kinds of suchmagnetic particles are used. These groups of magnetic particles are notseparately used, but used in combination, whereby the greater magneticparticles act so as to aid and facilitate the action of the smallermagnetic particles upon erasing of the resulting magnetophoretic displaysheet in such a manner that the greater magnetic particles aretemporally attracted by the smaller magnetic particles upon migrationand dispersion thereof to migrate in a state attached to the smallermagnetic particles, and the smaller magnetic particles migrate in astate included in the greater magnetic particles. As a result, cleanerasing is feasible without leaving the blackness of the smallermagnetic particles. According to the present invention, therefore, thepresent invention cab exhibit a particularly marked effect thatcharacters, diagrams and/or the like magnetically recorded on such amagnetic recording sheet can be partially erased simply and easily fromthe recording surface side. As described above, in the presentinvention, such actions and effects as described above are brought aboutby using, in combination, the magnetic particles having a particlediameter ranging from 0.1 μm to 1.0 μm as a group of the smallermagnetic particles and the magnetic particles having a particle diameterranging from greater than 1.0 μm to 20 μm as a group of the greatermagnetic particles. The effects of the present invention cannot beachieved if this range is departed.

With respect to the microcapsules used in the present invention, inwhich a liquid dispersion, a white pigment, additives and the magneticparticles are encapsulated, the average particle diameter is 50 to 650μm, preferably 50 to 400 μm. If the average diameter is smaller than 50μm, the effects of the present invention cannot be achieved. If theaverage particle diameter exceeds 650 μm on the other hand, economicaldisadvantage is incurred. The microcapsules themselves can be easilyproduced by means of any publicly known production technique. The liquiddispersion used in the present invention is composed of solvents stableto the production of the microcapsules and compatible with each other.As the liquid dispersion, a low-boiling solvent and a high-boilingsolvent may preferably used in combination for the purpose offacilitating the movement (migration) of a magnetic material (forexample, magnetic particles) and improving contrast. As described above,examples of the low-boiling solvents used in the present inventioninclude toluene, xylene, ethylbenzene, methylcyclohexane,ethylcyclohexane and cyclohexane. These low-boiling solvents may be usedeither singly or in any combination thereof. Examples of thehigh-boiling solvents used in the present invention includedodecylbenzene, dipentylbenzene, diphenyl ether, dibenzyl benzoate,diethyl phthalate, phenylxylylethane, diethylbenzene, pentylbenzene,ethyl phthalate and butyl phthalate. These high-boiling solvents may beused either singly or in any combination thereof. A proportion of thehigh-boiling solvent to the low-boiling solvent is 10 to 250 parts byweight per 100 parts by weight of the low-boiling solvent, preferably 20to 200 parts by weight per 100 parts by weight of the low-boilingsolvent, more preferably 20 to 150 parts by weight per 100 parts byweight of the low-boiling solvent, still more preferably 40 to 100 partsby weight per 100 parts by weight of the low-boiling solvent. If theproportion of the high-boiling solvent to the low-boiling solvent islower than 10% by weight, the divergence of the low-boiling solventcannot be prevented. Although mixing in a ball mill or the like isnecessary for dispersing the magnetic material and the white pigment ina solvent, only the low-boiling solvent high in volatility cannot beused in the mixing, and so it is necessary to mix at least 10% by weightof the high-boiling solvent. If the proportion of the high-boilingsolvent exceeds 250% by weight on the other hand, the movement of themagnetic particles becomes poor.

The white pigment used in the present invention is composed ofnonmagnetic particles. Examples thereof include white pigments such astitanium oxide, lithopone, zinc white, white lead and zinc sulfide. Thetitanium oxide used may be either anatase type and rutile type. Rutiletype titanium oxide is preferred from the viewpoint of coveringproperty. These pigments are preferably small in specific gravity.Further, those having relatively high oil absorption (meaning that asolvent is absorbed in the interior of particles) are preferred. Noparticular limitation is imposed on the particle diameter of thenonmagnetic particles so far as they can be sufficiently dispersed.However, it is generally 0.1 to 20 μm, preferably 0.1 to 10 μm, morepreferably 0.1 to 5 μm, still more preferably 0.1 to 1 μm. When theparticle diameter of the magnetic particles is great, and the particlediameter of titanium oxide is small, the blackness is not developedthough the movement of the magnetic particles becomes fast, so thatcontrast is deteriorated. When the particle diameter of the magneticparticles is small, and the particle diameter of titanium oxide isgreat, the movement of the magnetic particles becomes extremely poorthough the blackness is developed, and contrast is improved. Thus, sucha combination is not preferred. From these facts, it has been found thatthe size of the nonmagnetic particles is preferably smaller than themagnetic particles.

A proportion of the nonmagnetic particles used in the present inventionis 5.0 to 50.0% by weight, preferably 10.0 to 40.0% by weight, morepreferably 15.0 to 35.0% by weight based on the weight of the liquiddispersion. If the proportion of the nonmagnetic particles to the liquiddispersion is lower than 5.0% by weight, the resulting sheet becomesblackish as a whole in the case of a thin type in particular, and socontrast is not fully developed, and moreover clear characters and/orimages cannot be displayed. If the proportion of the nonmagneticparticles exceeds 50.0% by weight on the other hand, the resulting sheetbecomes whitish as a whole on the contrary, and so contrast is not fullydeveloped. In view of these respects, the proportion of the nonmagneticparticles to the magnetic particles is preferably 4 to 30 times, morepreferably 5 to 20 times, still more preferably 6.0 to 15.0 times. Theresulting sheet can thereby display clear images excellent in contrasteven in the case of a thin type.

Examples of the additives used in the present invention include fineparticle thickeners and dispersing agents. Examples of the fine particlethickeners include silicic anhydride, hydrous silicic acid, silicates(sodium silicate, potassium silicate, aluminum silicate, calciumsilicate, etc.), finely particulate alumina, silica powder, diatomaceousearth, kaolin, hard clay, soft clay, bentonite, ultrafine calciumcarbonate, ultrafine activated calcium carbonate, calciumhydrogencarbonate, hydrous basic magnesium carbonate, barium sulfate andbenzidine Yellow. These thickeners may be used either singly or in anycombination thereof. The amount of the fine particle thickener added tothe liquid dispersion varies according to the kind of the liquiddispersion. However, it generally 0.2 to 5% by weight, preferably 0.4 to2% by weight based on the weight of the liquid dispersion. If the amountof the fine particle thickener added to the liquid dispersion is lessthan 0.2% by weight, the adjusting effect of such a thickener on themagnetic particles and the nonmagnetic particles cannot be exhibited. Onthe other hand, any amount exceeding 5% by weight interferes with themovement of solid particles such as the magnetic particles. It is hencenot preferable to add the thickener in such a little or great amount.

The dispersing agent used in the present invention is used in dispersingthe magnetic particles and the like. Examples of preferable dispersingagents include polyoxyethylene lauryl ether, polyoxyethylene cetylether, polyoxyethylene stearyl ether, polyoxyethylene oleyl ether,anionic fatty acid ester mixtures, polycarboxylic acid amine salts,sorbitan trioleate, sorbitan monolaurate and sorbitan monostearate. Theamount of the dispersing agent added may be an amount ordinarily addedas a dispersing agent. However, it is generally 0.2 to 10% by weight,preferably 0.4 to 3.0% by weight based on the liquid dispersion. If theamount of the dispersing agent added is less than 0.2% by weight,sufficient dispersing effect cannot be achieved. If the amount exceeds10% by weight on the other hand, the viscosity of the liquid dispersionbecomes high, and so the properties of the liquid dispersion areimpaired.

In addition, colorants may be added to the liquid dispersion as needed.As the colorants, dyes and pigments are generally used. Examples of thedyes and pigments include dyes such as Methylene Blue, Congo Red andBenzo Yellow TZ, and besides Oil Blue, Oil Green, Oil Yellow andBenzidine Yellow. Such a colorant may be contained in any of a gelatinfilm of a microcapsule, a transparent aqueous additive in a microcapsulecoating layer and a transparent film, to say nothing of the liquiddispersion in the microcapsules, whereby the microcapsules can becolored proper color. A back surface or background of a magnetic displaypanel can be thereby colored various colors.

In the front face erasable microcapsule magnetophoretic display sheetsdescribed above, the proportion of the magnetic particles is the sumtotal of 100% by weight of at least one kind of the magnetic particles(hereinafter referred to as “small particles”) having a particlediameter ranging from 0.1 μm to 1.0 μm and 10 to 200% by weight of atleast one kind of the magnetic particles (hereinafter referred to as“large particles”) having a particle diameter greater than the aboveparticles ranging from greater than 1.0 μm to 20 μm. A proportion of thelarge particles to the small particles is preferably 50 to 150% byweight, more preferably 80 to 120% by weight per 100% by weight of thesmall particles. If the proportion of the large particles is lower than10% by weight, the movement of the small particles cannot besufficiently aided. If the proportion of the large particles exceeds200% by weight on the other hand, blackness cannot be sufficientlydeveloped, so that clear characters and/or diagrams cannot be displayed.Accordingly, the present invention can exhibit an excellent effect thatcharacters, diagrams and/or the like magnetically recorded can be simplyand easily erased partially from the recording surface side by adjustingthe proportions of the small particles and the large particles to 10 to200% by weight per 100% by weight of the small particles, particularly50 to 150% by weight per 100% by weight of the small particles.

In the front face erasable microcapsule magnetophoretic display sheetsaccording to the present invention, the support is a releasing member,and the display sheet is composed of only a support-free soliddispersion layer from which the releasing member has been released andremoved, whereby the uses of the sheets can be variously widened withoutusing any writing magnet pen in that they can be used for production ofmachine readable magnetic records and as inspection materials of steelproducts or the like.

In the erasing magnet for front face erasing according to the presentinvention, which is adapted to slide it over at least a part of thefront face of the front face erasable microcapsule magnetophoreticdisplay sheet, the magnet is arranged and used in such a manner that aclearance is made between the front face erasable microcapsulemagnetophoretic display sheet and the magnet. The principle of theerasing magnet for front face erasing according to the present inventionwill hereinafter be described. The erasing magnet for front face erasingmeans a magnet capable of erasing characters, diagrams and/or the likemagnetically recorded on the front face of the front face erasablemicrocapsule magnetophoretic display sheet by sliding the erasing magnetover the front face of the display sheet from the displayed surfaceside. This magnet emits countless magnetic lines from its N pole towardits S pole to form a magnetic field. In these magnetic lines, there areportions almost horizontally acting on the magnet at a position somewhatdistant from the magnet. A region of the almost horizontally actingmagnetic lines is caused to act on the microcapsules in the microcapsulemagnetophoretic display sheet, whereby the magnetic particles in themicrocapsules are moved and dispersed by the action of the magneticlines. As a result, the nonmagnetic particles composed of the whitepigment particles are substitutively gathered in plenty at the surfaceon the front face side to exhibit a white color. The present inventorshave paid attention to the fact that this almost horizontally actingmagnetic field is generated only by selecting an erasing magnet havingthe desired nature, and this nature is very weak.

According to the erasing magnet of the present invention, by taking suchthe construction as described above, an erasing magnet which has asimple structure and can wholly or particularly partially erasecharacters, diagrams and/or the like from the recording surface side ofa recorded sheet with ease by causing a magnetic field different fromthe case where a magnet is brought into direct contact with the sheet,i.e., with the generation of a magnetic field controlled, to act on themicrocapsules in the sheet can be provided. As a material for themagnet, ferrite, rare earth metals, Alnico alloy or the like may beused. However, the material for the magnet is not limited to thesematerials.

The erasing magnet for front face erasing according to the presentinvention will be described in more detail. An erasing magnet having aproperty value of 100 to 750 G in terms of surface magnetic flux densityis preferably used. A magnet used herein varies according to the uses ofthe display sheet, and so it is widely selected according to the usesthereof without any particular limitations. Its form may be any form ofcylinder, coin, rod, prism and the like, and its size may be suitablyselected. As erasing magnets used in front face erasing, are preferredferrite magnets, rare earth magnets such as rare earth cobalt magnets(for example, samarium.cobalt magnet) and rare earth iron magnets(neodymium.iron magnet, etc.), and bond magnets. As the kind ofmagnetization of the magnet, is prepared double-side magnetization IP(the surface magnetic flux density amounts to 100 to 750 G under theseconditions). As a particularly preferable magnet, may be used anisotropic or anisotropic rare earth magnet or ferrite magnet. Clearerasing is feasible by selecting a magnet and the kind of magnetizationof such conditions. In the erasing magnet for front face erasing used inthe present invention, it is preferred to control the generation of amagnetic field by providing a clearance. A clearance distance is oftendetermined by the material of the magnet used. No particular limitationis imposed on a method for providing the clearance. For example, eitheran air layer or a nonmagnetic material may be provided between the frontface erasable microcapsule magnetophoretic display sheet and the magnetof the erasing magnet. In the present invention, a method of uniting themagnet to the nonmagnetic material is preferred.

No particular limitation is imposed on the nonmagnetic material.However, preferable examples thereof include resins, sponge or spongeresins, rubber, wood, corrugated board, paper, fibers, glass and metals.These materials may be preferably capable of smoothly sliding on themagnetic display sheet. As a method for uniting the magnet to thenonmagnetic material, may be either bonding or fitting, or integralmolding between different materials in the case of resins or rubber. Theclearance may also be provided either on the erasing surface side aloneor on both sides thereof. When the clearance is provided on both sides,there is no need to distinguish the erasing side of the magnet. When theclearance is provided on all the surfaces of the magnet, recessesconformed to fingers or a lug or handle may preferably be provided tomake handling easy.

FIGS. 1A and 1B are a plan view and a cross-sectional view,respectively, illustrating an erasing magnet for front face erasing anda front face erasable microcapsule magnetophoretic display sheetaccording to an embodiment of the present invention, in which FIG. 1A isa plan view showing the erasing magnet for front face erasing, and FIG.1B is a cross-sectional view showing the erasing magnet for front faceerasing and the front face erasable microcapsule magnetophoretic displaysheet. FIGS. 2A and 2B are a plan view and a cross-sectional view,respectively, illustrating the front face erasable microcapsulemagnetophoretic display sheet and an erasing magnet for front faceerasing according to another embodiment of the present invention, inwhich FIG. 2A is a plan view showing the erasing magnet for front faceerasing according to another embodiment, and FIG. 2B is across-sectional view showing the front face erasable microcapsulemagnetophoretic display sheet and the erasing magnet for front faceerasing. FIG. 1A illustrates the erasing magnet I for front face erasinghaving a circular section and a diameter, φ₁ of 10 to 100 mm. Asillustrated in FIG. 1B, the erasing magnet I for front face erasing hasa clearance 3 on a lower surface of a magnet 2 for erasing and comesinto contact with a front face 1 a of the front face erasablemicrocapsule magnetophoretic display sheet 1 through the clearance 3. Inthis embodiment, the thickness, z of the magnet 2 for erasing is 2 to 20mm, and the thickness, z′ of the clearance is expressed by 0.2Z to 20Z.Similarly, FIG. 2A illustrates the erasing magnet II for front faceerasing having a rectangular section and a size of 10 to 100 mm inbreadth, x and 10 to 100 mm in length, y. As illustrated in FIG. 2B, theerasing magnet II for front face erasing has a clearance 3 on a lowersurface of a magnet 2 for erasing. In this embodiment, the values of zand z′ are the same as in FIG. 1B.

As illustrated in FIGS. 1A to 2B, the diameter, φ₁ is 10 to 100 mm, x is10 to 100 mm, and y is 10 to 100 mm, and no particular limitation isimposed on the shape and size of the erasing magnets I and II for frontface erasing so far as the dimensions fall within the respective rangesdescribed above. The values of φ₁, x and y are can be determined can bedetermined according to the sizes of the front face erasablemicrocapsule magnetophoretic display sheet 1 used and characters to bewritten thereon. Z is 2 to 20 mm, and z′ is 0.2Z to 20Z, preferably 0.2zto 5.0z, more preferably 0.5z to 2.0z, most preferably 0.5z to 1.0z. Ifz is out of the range of 2 to 20 mm, handling is difficult in view ofthe size, weight, etc. If z′ is smaller than 0.2z, a magnetic fieldapplied to the front face erasable microcapsule magnetophoretic displaysheet 1 comes near to perpendicular, and so the surface of the sheetbecomes blackish. If z′ exceeds 20z on the other hand, no magnetic fieldcan be applied to the front face erasable microcapsule magnetophoreticdisplay sheet 1, and so written characters cannot be erased. Such asmall or great clearance is hence not preferred. In these limitations,z′ is particularly important from the viewpoint of causing the magneticfield to suitably act on the magnetic display sheet.

FIGS. 3A and 3B illustrate a writing magnet III for front face erasablesheet according to the present invention. As illustrated in FIG. 3A, awriting magnet 21 is covered with a metal 5 to control a magnetic field.More specifically, it is a publicly known technique to cover a magnetwith a metal such as brass or iron to partially control the generationof a magnetic field, whereby fine and clear written characters can beformed on a magnetic display sheet like the conventional writing magnet.In the writing magnet III for front face erasable sheet used for thefront face writable and erasable magnetic display sheet (i.e. the frontface erasable microcapsule magnetophoretic display sheet) according tothe present invention, however, the generation of a magnetic field mustbe more severely controlled than the front face writable and rear faceerasable magnetic display sheet. In the writing magnet III used in thepresent invention, as a material of a magnet 21 for writing, ferrite,rare earth metals, Alnico alloy or the like may be used. However, thematerial for the magnet 21 is not limited to these materials. Morespecifically, as the kind of magnetization of the magnet 21 for writing,is prepared double-side magnetization IP (the surface magnetic fluxdensity amounts to at least 750 G under these conditions). In order toproduce the writing magnet III for front face erasable sheet using sucha magnet 21 for writing, the tip of the magnet 21 for writing is coatedwith a metal 5 composed of a ferromagnetic material. A magnetic forcedistribution can be thereby more concentrated, and so a clear record canbe effectively provided. As the coating metal 5, is generally preferablyused brass or iron excellent in working ability and stability. However,the material is not limited to these metals so far as it can easilycontrol a magnetic field.

The writing magnet for front face erasable sheet according to thepresent invention will be described in more detail. FIGS. 3A and 3B area plan view and a cross-sectional view, respectively, illustrating thewriting magnet for front face erasable sheet used in the presentinvention. As illustrated in FIGS. 3A and 3B, the writing magnet III forfront face erasable sheet is composed of a rod magnet 21 having adiameter of φ₂, and coated with the metal 5 under such conditions thatan angle formed between a diameter, φ₂′ of a coating on the tip portionand a diameter of a coating on the rear end is θ.

With respect to the shape and size of the magnet for writing used inproducing the writing magnet III for front face erasable sheet, φ₂ is0.2 to 2.0 mm, preferably 0.8 to 1.2 mm. φ₂′ is 1.0φ₂ to 4.0φ₂ mm,preferably 2.0φ₂ to 3.0φ₂. If φ₂ is smaller than 0.2 mm, and φ₂′ issmaller than 1.0φ₂, working is difficult, strength becomes insufficient,and no preference is given even from the viewpoint of safety. If φ₂exceeds 2.0 mm on the other hand, a magnetic field generated by such amagnet becomes too great, and so characters written by the resultingwriting magnet becomes thick. In FIG. 3B, z is 5.0 to 10.0 mm, and z′ is−0.3 to 1.0 mm, preferably 0.0 to 0.5 mm. If φ₂′ is out of the range of1.0φ₂ to 4.0φ₂ mm, and z′ is out of the range of −0.3 to 1.0 mm, it isimpossible to control the magnetic field to a desired value, and sowritten characters become unclear. Any z′ greater than 1.0 mm is notpreferred even from the viewpoint of safety. No particular limitation isimposed on z, and z is preferably matched to a pen body. No particularlimitation is also imposed on θ. In these requirements, z′ isparticularly important from the viewpoint of controlling the magneticfield. By satisfying these conditions, the writing magnet III for frontface erasable sheet can exhibit an excellent effect that finecharacters, diagrams and/or the like can be clearly displayed.Incidentally, the metal coating 5 is provided for the purpose ofconcentrating a magnetic force distribution, and so the coating form ofthe metal 5 can be optionally determined by tests and the like.

The front face erasable microcapsule magnetophoretic display sheetsaccording to the present invention can be used in various applicationfields, for example, cards such as cash cards, cashless cards, creditcards and prepaid cards, and besides general uses, for example,illustrated books for little children, toys for little children,character drills, panels for various games, boards for penmanship,sheets and boards having an adhesive layer on their rear faces, boardsfor writing memos, black boars for meeting, various information boardsin clean rooms, sign boards with lamp, display panels for personalcomputers, etc. As special uses, they can be used for production ofmachine readable magnetic records and as inspection materials of steelproducts or the like.

The present invention will hereinafter be described in more detail bythe following examples. However, the following examples are intended toexplain the present invention, and so the present invention is notlimited to these examples.

EXAMPLE 1

(1) Preparation Process of Microcapsules: [Formulation of LiquidDispersion A to be encapsulated in microcapsule] Smaller magneticparticle (synthetic 1.5 wt. % iron oxide, 0.3 μm) Greater magneticparticle (synthetic 1.5 wt. % iron oxide, 3 μm) Nonmagnetic particle(white titanium 12.0 wt. % oxide powder, R-820, 0.26 μm, product ofIshihara Sangyo Kaisha, Ltd.) High-boiling solvent (dibutyl phthalate)40.0 wt. % Low-boiling solvent (toluene) 43.6 wt. % Antifoaming agent(Dappo SN-350, 0.2 wt. % silicone, product of San Nopco Limited)Suspending agent (finely particulate 0.5 wt. % silicic acid, Aerosil,product of Nippon Aerosil Co., Ltd.) Dispersing agent (Nopcosanto K9630.7 wt. % product of San Nopco Limited)

A 3.6% aqueous solution of gum arabic was added to a 3.6% aqueoussolution of gelatin adjusted to pH 6 to prepare an aqueous solution formicrocapsule film. After the solution was heated to about 50° C., andthe pH of the solution was adjusted to 5, Liquid Dispersion A formulatedabove was added, and the resultant mixture was stirred in such a mannerthat the average droplet diameter of droplets of the dispersion amountsto 100 μm. After the desired dispersion droplets were obtained, thedispersion was slowly cooled to 10° C. to gel a polymer film ofgelatin/gum arabic deposited interfaces between the dispersion droplets.A 25% aqueous solution of glutaraldehyde was added to cure the polymerfilm to obtain gelatin microcapsules. The microcapsule thus obtainedwere classified through a screen to remove particles of a size exceeding250 μm, thereby obtaining microcapsules having a particle diameter of250 μm or smaller.

(2) Production of Front Face Erasable Microcapsule MagnetophoreticDisplay Sheet:

An aqueous solution of a urethane resin as a aqueous binder was added toa group of microcapsules obtained by removing water from themicrocapsules obtained above, and the resultant mixture was fullystirred to form an inky product for coating. The viscosity of this inkyproduct for coating was 4,000 cPs. The thus-obtained inky product forcoating was applied to the surface of a transparent film having athickness of 75 μm and dried with hot air of 70° C. for 40 minutes. Thethickness of the microcapsule-containing coating layer was 250 μm. As aprotective member, a polyethylene terephthalate film having a thicknessof 50 μm was further bonded to the microcapsule-containing coating layerwith an adhesive to produce a microcapsule magnetic display sheet.

(3) Production of Erasing Magnet for Front Face Erasing:

An erasing magnet was formed in the shape of a coin as illustrated inFIG. 1A using ferrite as a material of the magnet. The diameter φ₁ andthickness z thereof were determined to be 30 mm and 3.0 mm,respectively. On the other hand, an ABS resin(acrylonitrile.butadiene.styrene resin) was used as a material of aclearance to form a clearance having a diameter φ₁ of 30 mm and athickness z′ of 2.0 mm in the shape of a coin. The coin-shaped ferriteand the coin-shaped ABS resin were then integrally bonded to each otherto provide an erasing magnet I for front face erasing.

(4) Production of Writing Magnet for Front Face Erasable Sheet:

A circular rod-shaped ferrite magnet 21 was coated with brass 5 asillustrated in FIGS. 3A and 3B, thereby producing a writing magnet IIIfor front face erasable sheet. A diameter of the magnet φ₂ and adiameter φ₂′ of a coating on the tip portion were 1.0 mm and 2.5 mm,respectively, and z and z′ were 7.0 mm and 0.0 mm, respectively. Ahandle was attached thereto to provide a writing magnet pen for frontface erasable sheet.

(5) Evaluation of Front Face Erasable Microcapsule MagnetophoreticDisplay Sheet:

The erasing magnet I for front face erasing was slid on the wholedisplay surface of the front face erasable microcapsule magnetophoreticdisplay sheet 1 to erase the whole display surface into a uniform clearwhite surface. Characters were written on this surface with the writingmagnet pen for front face erasable sheet. As a result, both greatermagnetic particles and smaller magnetic particles migrated on the frontface side to obtain a black clear written display. In order to erase apart of the recorded characters, the erasing magnet I for front faceerasing was brought into contact with the written display and scanned ona portion to be erased. As a result, the characters of the scannedregion were able to be cleanly erased to make the scanned region auniform clear white surface.

EXAMPLE 2

(1) Preparation Process of Microcapsules: [Formulation of LiquidDispersion B to be encapsulated in microcapsule] Smaller magneticparticle (synthetic 1.5 wt. % iron oxide, 0.3 μm) Greater magneticparticle (synthetic 1.0 wt. % iron oxide, 3 μm) Greater magneticparticle (synthetic 0.5 wt. % iron oxide, 10 μm) Nonmagnetic particle(white titanium 12.0 wt. % oxide powder, R-820, 0.26 μm, product ofIshihara Sangyo Kaisha, Ltd.) High-boiling solvent (dibutyl phthalate)40.0 wt. % Low-boiling solvent (toluene) 43.6 wt. % Antifoaming agent(Dappo SN-350, 0.2 wt. % silicone, product of San Nopco Limited)Suspending agent (finely particulate 0.5 wt. % silicic acid, Aerosil,product of Nippon Aerosil Co., Ltd.) Dispersing agent (Nopcosanto K9630.7 wt. % product of San Nopco Limited)(2) Production of Front Face Erasable Microcapsule MagnetophoreticDisplay Sheet:

Microcapsules were prepared in the same manner as in Example 1 exceptthat Liquid Dispersion B was used, and a front face erasablemicrocapsule magnetophoretic display sheet was produced in the samemanner as in Example 1 except that the microcapsules obtained above wereused.

(3) Evaluation of Front Face Erasable Microcapsule MagnetophoreticDisplay Sheet:

Such an erasing magnet II for front face erasing as illustrated in FIG.2A was slid on the whole display surface of the front face erasablemicrocapsule magnetophoretic display sheet 1 to erase the whole displaysurface into a uniform clear white surface. Characters were written onthis surface with the writing magnet pen for front face erasable sheet.As a result, a black clear written display was obtained. In order toerase the whole of the recorded characters, the erasing magnet II forfront face erasing was brought into contact with the display surface andscanned over the whole surface. As a result, the whole display surfacewas able to be made a uniform clear white surface. The conventionalerasing magnet was also slid on the whole display surface of the frontface erasable microcapsule magnetophoretic display sheet 1. As a result,the surface did not become white and entirely remained blackish(blackish gray). Comparative Example 1:

(1) Preparation Process of Conventional Microcapsules: [Formulation ofLiquid Dispersion C to be encapsulated in microcapsule] Smaller magneticparticle (synthetic 3.0 wt. % iron oxide, 0.3 μm) Nonmagnetic particle(white titanium 12.0 wt. % oxide powder, R-820, 0.26 μm, product ofIshihara Sangyo Kaisha, Ltd.) High-boiling solvent (dibutyl phthalate)40.0 wt. % Low-boiling solvent (toluene) 43.6 wt. % Antifoaming agent(Dappo SN-350, 0.2 wt. % silicone, product of San Nopco Limited)Suspending agent (finely particulate 0.5 wt. % silicic acid, Aerosil,product of Nippon Aerosil Co., Ltd.) Dispersing agent (Nopcosanto K9630.7 wt. % product of San Nopco Limited)(2) Production of Conventional Microcapsule Magnetophoretic DisplaySheet:

Microcapsules were prepared in the same manner as in Example 1 exceptthat Liquid Dispersion C was used, and a conventional microcapsulemagnetophoretic display sheet was produced in the same manner as inExample 1 except that the microcapsules obtained above were used.

(3) Evaluation of Conventional Microcapsule Magnetophoretic DisplaySheet:

An erasing magnet II for front face erasing (see FIGS. 2A and 2B) wasslid on the whole rear face of the conventional microcapsulemagnetophoretic display sheet. As a result, the front face exhibited awhite color. When characters were then written on this surface with thewriting magnet pen for front face erasable sheet, a black clear writtendisplay was obtained like Example 1. When the erasing magnet II forfront face erasing was brought into contact with the whole displaysurface and scanned over the whole surface, however, the display surfacewas extremely blackish (blackish gray). When characters were thenwritten on this surface with the writing magnet pen for front faceerasable sheet, written characters were very poor in contrast, and sothe resultant written display was entirely poor in utility. Characterswere further written with a conventional writing magnet pen after theerasing magnet II for front face erasing was slid on the whole rear faceof the conventional microcapsule magnetophoretic display sheet to erasethe display surface clean. As a result, the resultant written displayslightly had an unclear portion, but caused no problems in practicaluse.

COMPARATIVE EXAMPLE 2

(1) Preparation Process of Conventional Microcapsules: [Formulation ofLiquid Dispersion D to be encapsulated in microcapsule] Greater magneticparticle (synthetic 3.0 wt. % iron oxide, 3 μm) Nonmagnetic particle(white titanium 12.0 wt. % oxide powder, R-820, 0.26 μm, product ofIshihara Sangyo Kaisha, Ltd.) High-boiling solvent (dibutyl phthalate)40.0 wt. % Low-boiling solvent (toluene) 43.6 wt. % Antifoaming agent(Dappo SN-350, 0.2 wt. % silicone, product of San Nopco Limited)Suspending agent (finely particulate 0.5 wt. % silicic acid, Aerosil,product of Nippon Aerosil Co., Ltd.) Dispersing agent (Nopcosanto K9630.7 wt. % product of San Nopco Limited)(2) Production of Conventional Microcapsule Magnetophoretic DisplaySheet:

Microcapsules were prepared in the same manner as in Example 1 exceptthat Liquid Dispersion D was used, and a conventional microcapsulemagnetophoretic display sheet was produced in the same manner as inExample 1 except that the microcapsules obtained above were used.

(3) Evaluation of Conventional Microcapsule Magnetophoretic DisplaySheet:

An erasing magnet II for front face erasing was slid on the wholedisplay surface of the conventional microcapsule magnetophoretic displaysheet. As a result, the surface exhibited a blackish gray color. Whencharacters were then written on this surface with the writing magnet penfor front face erasable sheet, only a written display very low incontrast was obtained. The same result was obtained even when characterswere written with a conventional writing magnet pen. A conventionalerasing magnet was slid on the whole display surface of the conventionalmicrocapsule magnetophoretic display sheet to wholly erase the displaysurface. However, the display surface remained black as a whole.Characters were written on this display surface with the writing magnetpen for front face erasable sheet and the conventional writing magnetpen. In any case, however, no character was unable to be written.

EXAMPLES 3 AND 4

Production of Erasing Magnet (Coin Shape) for Front Face Erasing:

Erasing magnets were respectively produced with materials and in sizesshown in Table 1 in the form of a coin as illustrated in FIG. 1A. Theyare shown in Table 1 together with Comparative Examples. TABLE 1 Ex. 3Comp. Ex. 3 Ex. 4 Comp. Ex. 4 Coin-shaped Component of magnet Erasingmagnet A Erasing magnet C Erasing magnet E Erasing magnet G Material ofmagnet Ferrite Ferrite Ferrite Ferrite Diameter φ₁(mm) 30 30 30 30Thickness z(mm)  3.0  3.0  3.0  3.0 Material of clearance ABS resin —ABS resin ABS resin Diameter φ₁ (mm) 30 — 30 30 Thickness z′(mm)  3.0  0(direct contact)  0.6 63 Uniting method of both Bonding — BondingBonding

When the erasing magnet A for front face erasable sheet according to thepresent invention was used to erase a written display recorded on afront face erasable microcapsule magnetophoretic display sheet, thewritten display was able to be very clearly erased, the display surfacewas visually observed becoming clear white. In addition, no unevennessoccurred. When the comparative erasing magnet E was used, a writtendisplay was able to be erased, but the surface was somewhat blackish.Therefore, contrast was slightly lowered. However, no problem wasoffered in practical use though unevenness slightly occurred. On theother hand, the comparative erasing magnet G failed to erase a writtendisplay. The comparative erasing magnet C was able to erase a writtendisplay, but the display surface became very blackish, and so contrastwas very lowered, which caused a problem in practical use. In addition,unevenness was heavy.

EXAMPLES 5 AND 6

Production of Erasing Magnet (Rectangle) for Front Face Erasing:

Erasing magnets were respectively produced with materials and in sizesshown in Table 2 in the form of a rectangle as illustrated in FIG. 2A.They are shown in Table 2 together with Comparative Examples. TABLE 2Ex. 5 Comp. Ex. 5 Ex. 6 Comp. Ex. 6 Coin-shaped Component of magnetErasing magnet B Erasing magnet D Erasing magnet F Erasing magnet HMaterial of magnet Rare earth Rare earth Rare earth Rare earth Breadthx(mm) 50 50 50  50 Length y(mm) 30 30 30  30 Thickness z(mm) 15 15 15 15 Material of clearance Syn. rubber — Syn. rubber Syn. rubber Breadthx(mm) 50 50 50  50 Length y(mm) 30 30 30  30 Thicknesss z′(mm) 15  0(direct contact)  3.0 330 Uniting method of both Integral molding —Integral molding Integral molding

When the erasing magnet B for front face erasable sheet according to thepresent invention was used to erase a written display recorded on afront face erasable microcapsule magnetophoretic display sheet, thewritten display was able to be very clearly erased, the display surfacewas visually observed becoming clear white. In addition, no unevennessoccurred. When the comparative erasing magnet F was used, a writtendisplay was able to be erased, but the surface was somewhat blackish.Therefore, contrast was slightly lowered. However, no problem wasoffered in practical use though unevenness slightly occurred. On theother hand, the comparative erasing magnet H failed to erase a writtendisplay. The comparative erasing magnet D was able to erase a writtendisplay, but the display surface became very blackish, and so contrastwas very lowered, which caused a problem in practical use. In addition,unevenness was heavy.

EXAMPLE 7

Production of Writing Magnet for Front Face Erasable Sheet:

Writing magnets for front face erasable sheet were respectively producedwith materials and in sizes shown in Table 3 by coating each writingmagnet with a metal as illustrated in FIGS. 3A and 3B. A handle wasattached to each writing magnet to provide a writing magnet pen forfront face erasable sheet. TABLE 3 Component of magnet Writing magnet AWriting magnet B Writing magnet C Brass Material of magnet Ferrite Rareearth Ferrite Diameter φ₂ (mm) 1.0 1.2 1.0 Diameter φ₂′ (mm) 2.5 2.4 2.5z (mm) 7.0 6.0 7.0 z′ (mm) 0.0 0.2 No coated Component of magnet Writingmagnet D Writing magnet E Writing magnet F Brass Material of magnet Rareearth Ferrite Rare earth Diameter φ₂ (mm) 1.2 1.0 1.2 Diameter φ₂′ (mm)2.4 2.5 2.4 z (mm) 6.0 7.0 6.0 z′ (mm) No coated 2.0 1.8 Component ofmagnet Writing magnet G Writing magnet H Writing magnet I Brass Materialof magnet Ferrite Rare earth Rare earth Diameter φ₂ (mm) 1.0 1.2 2.5Diameter φ₂′ (mm) 2.5 2.4 4.5 z (mm) 7.0 6.0 6.0 z′ (mm) −0.5 −0.4 0.0

The writing magnets A and B for front face erasable sheet wererespectively used to conduct recording on a front face erasablemicrocapsule magnetophoretic display sheet. As a result, both largecharacters and small characters recorded thereon were very clear. Whenthe writing magnets E, F, G, H and I for front face erasable sheet wererespectively used to conduct recording on a front face erasablemicrocapsule magnetophoretic display sheet, large characters were clear,but small characters were somewhat unclear. However, they caused noproblem in practical use. When the writing magnets C and D for frontface erasable sheet were respectively used to conduct recording, bothlarge characters and small characters were unclear. In particular,intersecting portions of the characters were indistinct.

According to the present invention, as described above, in the frontface erasable microcapsule magnetophoretic display sheet, comprising thesupport and the solid dispersion layer provided on one surface of thesupport and composed of the microcapsules having an average particlediameter of 50 to 650 μm, in which the liquid dispersion, the whitepigment, the additives and the magnetic particles are encapsulated, andthe binder, the magnetic particles include at least two kinds ofmagnetic particles different in particle diameter from each other,whereby the magnetic sheet can exhibit a particularly marked effect thatcharacters, diagrams and/or the like magnetically recorded on themagnetic recording sheet can be wholly or partially erased simply andeasily from the recording surface side thereof.

In the erasing magnet for front face erasing according to the presentinvention, which is adapted to slide it over at least a part of thefront face of a front face erasable microcapsule magnetophoretic displaysheet, the magnet is arranged and used in such a manner that a clearanceis made between the front face erasable microcapsule magnetophoreticdisplay sheet and the magnet, whereby a magnetic field different fromthe case where the magnet is brought into direct contact with the sheetacts on microcapsules in the sheet. As a result, an erasing magnet forfront face erasing, which has a simple structure and can partially erasecharacters, diagrams and/or the like from the recording surface side ofa recorded sheet can be provided.

In the writing magnet for front face erasable sheet according to thepresent invention, the magnet is covered with a metal to control amagnetic field, whereby the writing magnet can exhibit an excellenteffect that fine characters, diagrams and/or the like can be clearlydisplayed.

1-6. (canceled)
 7. A writing magnet for front face erasable microcapsulemagnetophoretic display sheets, wherein the magnet is covered with ametal to control a magnetic field, the magnet comprising: a tip; a rearend; a coating around the tip; a coating around the base, wherein thetip is exposed, and the tip extends above the coating around the tip bybetween 0 and 1.0 mm. 8-36. (canceled)
 37. The writing magnet of claim7, wherein the tip has a diameter of between 0.2 mm and 2.0 mm, and thecoating around the tip plus the tip has a diameter of between 0.2 mm and8.0 mm.
 38. The writing magnet of claim 37, wherein the tip has adiameter between 0.8 mm and 1.2 mm.
 39. The writing magnet of claim 7,wherein the tip extends above the coating around the tip by between 0 mmand 0.5 mm.
 40. The writing magnet of claim 7, wherein the tip isselected from ferrite, rare earth metal, or Alnico alloy.
 41. Thewriting magnet of claim 40, wherein the coating is selected from brassor iron.
 42. The writing magnet of claim 41, wherein the tip has asurface magnetic flux density of at least 750 G.